In general, an electronic endoscope includes imaging means such as an imaging device for applying illumination light of R (red), G (green), and B (blue) with various wavelengths to a subject in a time series manner and then photoelectrically converting light reflected by the subject into video signals using a solid-state image sensor such as a charge coupled device (CCD). This type of imaging device has the following disadvantage: When the subject moves fast, three color component signals obtained in time series are shifted. In other words, color shift occurs.
To reduce color shift, color shift reducing apparatuses for receiving color video signals from a field-sequential imaging device and reducing color shift of the color video signals have been proposed.
The color shift reducing apparatuses include a color shift reducing apparatus for applying a mean color component of the whole of an image with color shift to a color shift part, thus correcting the color shift, and a color shift reducing apparatus for forming a correction color using a brightness component and color components of an image and then applying the correction color to a color shift part, thus correcting the color shift as disclosed in Japanese Unexamined Patent Application Publication No. 3-270392.
Japanese Unexamined Patent Application Publication No. 6-319694 discloses an apparatus for extracting the highest pixel frequency value from a color distribution histogram and assigning a color having the highest pixel frequency value as an estimated color to a color shift area, thus correcting color shift.
In addition, Japanese Unexamined Patent Application Publication No. 9-74570 discloses a color shift correcting apparatus for changing the combination ratio of an original image and a color shift corrected image in response to the conditions of the image to form a color shift reduced image. The apparatus can correct an image derived on undesirable processing conditions, for example, upon bleeding or spreading a stain., thus forming a natural color shift reduced image.
In each of the above-mentioned conventional color shift reducing apparatuses, however, each algorithm is established on the precondition that one pigment exists in a living body. Disadvantageously, when blood comes out a mucous membrane sprayed with a stain, namely, two or more pigments exist in a living body, the color of the strain is corrected using the same color as that of the blood, alternatively, the color of the blood is corrected using the same color as that of the strain. When a fixed color is assigned to a color shift portion, the portion is corrected using an achromatic color.
The present invention is made in consideration of the above circumstances. An object of the present invention is to provide a color shift reducing apparatus capable of accurately estimating a correction color when two or more pigments exist in a living body.
Another object of the present invention is to provide a color shift reducing apparatus capable of favorably performing a color shift reducing process to a dark image having low color saturation.